docs: def log_histogram(self, step, tag, val):
          '''
          Write a histogram event.
  
          :param int step: Time step (x-axis in TensorBoard graphs)
          :param str tag: Label for this value
          :param numpy.ndarray val: Arbitrary-dimensional array containing
              values to be aggregated in the resulting histogram.
          '''
          hist = Histogram()
          hist.add(val)
          summary = Summary(value=[Summary.Value(tag=tag, histo=hist.encode_to_proto())])
          self._add_event(step, summary)